Production of nodular iron



V 1C6 Patented Apr. 18, 1961 PRODUCTION OF N ODULAR IRON Lester C.Creme, West Alexandria, Ohio, assignor to The Dayton Malleable IronCompany, Dayton, 'Ohio, a cor- K This invention relates to theproduction of nodular iron (as this term is presently understood asincluding an as-cast iron product of an originally essentially gray ironmix in which the graphitic carbon content thereof is precipitated in theform of nodules or spherulites instead of in the form of flake graphite)and, more particularly, to the production of such nodular iron castingsby a process including a special chilling addition step, in addition totreatment of the mix with a nodularizing agent and/or a preconditioningslag, for controlling and enhancing the graphitizing potential of themolten mix and the immediate readiness and responsiveness of the and thecarbon component thereof to precipitate into the desired nodular formupon pouring and cooling the casting in the mold.

It will be understood that, with molten iron mixes of the character towhich this invention relates, the carbon content may be considered asdissolved and as precipitating from solution during cooling of thecasting, and that it is this precipitation of graphitic carbon which itis desired to control into the nodular or spherulitic form in makingnodular'iron to achieve the enhanced physical properties of the castingattributable to the nodular microstructure thereof when cooled. Also,particularly in the commercial production of nodular iron castings, itmay be desired to add to the molten mix being treated a minimal amountof nodularizing agent, if only for cost or economy reasons, forcontrolling the precipitation of the graphitic carbon into the nodularform instead of the flake form. Similarly, particularly in largecommercial casting production where a plurality of castings are to bepoured from a single ladle of iron, it is important to have someassurance that the desired nodular microstructure will be obtained inall (not merely most) of the castings poured from the ladle since it maybe quite inexpedient to test each casting (usually by demolishing thecasting) to determine whether or not, in fact, the desired nodularmicrostructure was obtained.

If it is attempted to control and correlate these various factors by,for example, merely increasing the amount of carbon in the iron mix (orthe so-called carbon equivalen as reflected by .the combined carbon andsilicon contents of the mix), in order to increase the so-calledgraphitizing potentia of the mix by having available a more concentratedsolution of carbon from which precipitation thereof may more readilyoccur upon initial cooling of the mix, it may be discovered that anexcessive amount of carbon actually precipitates. That is, since thecarbon, as precipitated in the cooling metal, has a tendency to floatupwardly through the cooling iron in the mold, too great a carboncontent may result ina concentration of carbon in the top portion of thecasting, and even to such an extent that the physical properties of theiron matrix at such top portion of the casting may be less than desired.On the other hand, utilizing lower carbon contents, as with hypoeutecticmixes, may lead to a situation where the carbon content is suflicientlydilute that there may be difiiculty in obtaining the desired immediateand rapid and uniform precipitation of the carbon into agglomeratednodules, even when an undesirably large addition of nodularizing agentis utilized.

According to this invention, however, a system is provided whereby amolten iron mix is heated to a sufficiently high temperature forhandling in the foundry and for insuring that all the carbon present isactually in solution, and then suddenly chilled, while still molten, forincreasing the responsiveness of the mix at the time of nodularizingagent addition for precipitation of carbon as controlled by thenodularizing agent into the desired nodular microstructure, as, forexample, by adding to the molten mix in the ladle or just prior totreatment with the nodularizing agent a substantial quantity of solidmetal to achieve some sudden chilling of the molten mix as the addedmetal is melted by the residual heat in the mix.

One object of this invention is to provide a system for the productionof nodular castings of the character described in which the molten ironmix to be treated with a nodularizing agent is suddenly chilled asubstantial amount just prior to the addition of the nodularizing agentfor increasing the graphitizing potential of the mix and enhancing theresponsiveness or readiness with which carbon dissolved in the molteniron will precipitate in the cooling casting into the desired nodularform.

1 Another object of this invention is to provide, in a nodularizing ironproducing process of the character described, a chilling stepparticularly useful with iron mixes in the hypoeutectic range of carboncompositions whereby the responsiveness of the mix to nodular graphiteprecipitation is enhanced immediately prior to the addition of anodularizing agent and pouring of the castings into the molds.

A further object of this invention is to provide a nodular iron processof the character described whereby a substantial amount of cold metal isadded to the molten iron mix in the ladle and prior to a nodularizingaddition for enhancing the susceptibility of the mix to ready graphiteprecipitation therefrom during cooling and influencing thereof into anodular microstructure.

A still further object of this invention is to provide a nodular ironprocess of the character described whereby a substantial amount of coldmetal is added to the molten iron mix in the ladle and prior to anodularizing addition for enhancing the susceptibility of the mix toready graphite precipitation therefrom during cooling and infiuencingthereof into a nodular microstructure, and also including the steps ofadding silicon after the chilling step for further enhancing thegraphitizing potential of the mix.

Still another object of this invetnion is to provide a process for theproduction of nodular iron castings in which an essentially hypoeutecticiron mix is prepared for a ladle addition of nodularizing agent and at atemperature sufiiciently high for insuring that all carbon is insolution and for maintaining the fluidity of the mix as acquired by thehandling and pouring procedures of the foundry, and then chilling themix a substantial amount by the addition thereto of cold metal formelting therein prior to the addition of the nodularizing agent forenhancing the responsiveness and readiness with which the graphiticcarbon in the mix will precipitate in the cooling metal in the mold intothe desired nodular microstructure uniformly dispersed throughout thecasting and as influenced by the nodularizing agent.

Other objects and advantages of this invention will be apparent from thefollowing description and the appended claims.

There may be many instances where it is desired to utilize anessentially hypoeutectic molten iron mix for the production therefrom ofnodular iron castings, and particularly in instances where it may befound that higher carbon contents produce in the finished casting aflotation of excess carbon in the upperportion of the casting as itstands in the mold with concomitantly reduced physical properties insuch high carbon areas of the casting. In some situations, also, thecarbon equivalent (as well understood in this art as meaning the weightpercent of-carbon content plus one-third of the Weight percent ofsilicon) may be increased during the nodularizing process as by adesirable late addition of silicon in the ladle to increase thegraphitizing potential of the mix and/or the inclusion of suchsubstances as calcium silicide in or along with the added nodularizingagent.

It may also be found that the completeness with which a nodularmicrostructure is assured in a plurality of castings poured from asingle ladle may increase with higher carbon equivalents, perhapsbecause of the increased graphitizing potential resulting from suchhigher carbon equivalents. For example, even though a carbon equivalentof 4.0 be considered a hypoeutectic iron prior to adding thenodularizing agent, this may be high enough to as sure virtually 100%production of nodular microstructures with usual or conventionalnodularizing additions. Nevertheless, such a carbon equivalent may,indeed, produce, with certain section sizes in the casting and/or as aresult of an increased carbon equivalent picked up from the nodularizingaddition, an undesirable excess flotation of carbon in the upper portionof the casting. If, on the other hand, the carbon equivalent of themolten mixprior to nodularizing or late silicon treatment be held to avalue substantially less than 3.5, the desired graphitizing may not beobtained.

Particularly with commercial production of a large number of castings ona production basis, the routine possibility that some (however few) ofthe castings produced from any one melting may not achieve the desirednodular microstructure and/ or physical properties specifications is amatter of substantial disadvantage and one which may, indeed, transcendthe normal inspection or spot checking techniques in production foundry.practices. To the foregoing, also, should be added the thought that,with production foundry techniques, the molten mix is advantageouslyheated in the first instance to a temperature suificiently high forensuring that the carbon will initially be dissolved in the molten ironand, also, to ensure that there will be enough residual heat in the mixafter tapping from the furnace into the ladle to assure fluiditysufiicient, upon pouring, for the metal to run or fiow'into all thevarious interstices or cavities of the casting mold prior .tosolidification.

If the readiness or responsiveness of the molten mix to graphiteprecipitation be considered as, at least in part, a function of theconcentration of carbon dissolved in the iron solution, it might beconsidered possible to enhance the precipitation by maintaining themolten mix at a temperature not substantially higher than that at whichthe carbon would be expected to precipitate. Yet, particularly inproduction foundry practices for mass producing hundreds or thousands ofidentical small castings (as compared to custom founding of a singlepart for a single made-to-order machine), the standard productionfoundry handling techniques may require heating the metal initially to asubstantially higher temperature so that a desirable degree of fluidityof the molten metal will be maintained notwithstanding a substantialtime period as the metal is tapped from .the furnace and while it isbeing handled in the ladle and poured into the molds, etc.

Similarly, treating the routine and repeated accomplishment ofsatisfactory nodular iron results as,-at least in part, a function ofgraphitizing potential, or, otherwise stated, the actual tendency of thedissolved carbon to precipitate out of solution in the iron according toWell understood solution mechanics, one might consider instigating ornucleating the desired precipitation of even low carbon contents 'by thesudden or late addition of additional carbon or silicon to the moltenmix. As noted above, however, the advantages expected from such atreatment may well be outweighed by the disadvantages stemming fromincreasing the carbon content (or the silicon content) by suchnucleating treatment and particularly in cases Where a substantialadditional carbon or silicon component is added to the molten iron forother purposes as by a pretreatment slag or by the extra addition of asilicide as part of the nodularizing agent.

Satisfactory results according to this invention, however, are achievedby preparing a molten gray iron mix of a composition as may be desiredfor the final casting and for nodularizing treatment of the mix with anyparticular nodularizing agent desired and/or for handling according towhatever foundry techniques and practices are desired, and then addingto themolten mix, preferably upon tapping from the furnace into theladle, a substantial quantity (at least approximately 3% by weight andpreferably about 5% or more) of cold or solid metal for providing asudden chilling temperature reduction in the molten mix of the order ofF. and preferably F. or more at the time of making the ladle addition ofnodularizing agent and/or providing a new source of undissolved carbonto serve as a nucleating agent to encourage precipitation of dissolvedcarbon.

Whereas the mechanics of the effect of such treatment may not now, withcertainty, be completely understood, it is believed that such suddenchilling, resulting from utilization of residual heat in the molten mixto melt the solid metal added thereto, provides a ready instigation ofgraphite precipitation more or less uniformly throughout the mix, andmay also provide some actual or mechanical interjection into the mix ofundissolved carbon as a source of nuclei on which the precipitatingdissolved carbon can agglomerate, under the influence of thenodularizing agent, into the desired uniformly dispersed nodules orspherulites in the cooling metal in the mold, although the ultimateadvantages of this invention may not be achieved merely by adding anodularizing agent without the chilling. It is also preferred, accordingto this invention, to include a late addition of silicon, after theaddition of cold metal to the mix and after the nodularizing agentaddition, as giving further enhanced results, perhaps because ofcreating localized hypereutectic effects, even in an essentiallyhypoeutectic mix, as a further inducement to nucleation of theprecipitating graphite into the desired nodular microstructure. Suchadded silicon, also as will be understood, provides a further increaseof the carbon equivalent in the final composition.

Although the advantages of this invention are applicable to a widevariety of iron mix compositions as treated with a wide variety ofnodularizing agents, the results are, perhaps, most emphatic with massproduction foundry techniques utilizing hypoeutectic mixes having carbonequivalents of no more than 3.5 prior to treatment according to thisinvention and, particularly, when the desired nodularizing process mayinclude treatment of the molten mix with a carbon-containing slag priorto nodularizing and/or when the nodularizing agent may include asilicide or be accompanied by a late silicon addition desirable forother purposes, all of which would, as well understood, increase thecarbon equivalent in the cooling metal in the mold.

It may also be desired, for a number of reasons, to handle the moltenmetal as close as practicable to the desired pouring temperature thereofand, of course, not to go to the expense of heating the initial mix toany higher temperature than is required for the founding operation.Nevertheless, in order to get all the carbon into solution in the firstplace in the mix and adequately blend and treat the various componentsor raw materials from which the molten mix is originally made up, it

may be necessary, as a practical matter,.to heat the original melt to atemperature of, perhaps 2850 F. according to standard production foundrypractices.

As noted above, it is desired that the chilling effect of adding solidmetal to the molten mix produce a sudden reduction of temperature of theorder of 100 to 160 F.

or more. As also will be understood, from conventional experience in thefounding of nodular iron castings, a pouring temperature of at leastabout 2700 F. may be found necessary for pouring small and thin sectioncastings, in order to achieve the required amount of fluidity of themolten metal when poured into the mold, although pouring temperatures aslow as about 2300 F. are practicable for larger section castings.Similarly, also, the desired final carbon and silicon content of thefinished casting can be adjusted according to this invention and moreor.less independently of the effects to be expected from carbon orsilicon additions to the finished casting resulting from slag treatmentsof the molten mix and/or silicon additions with or as a part of thenodularizing agent, since the desired propensity for graphitizing isenhanced by the chilling step also more or less independently of thegraphitizing potential inherent in the molten mix tapped from thefurnace. As will be noted, the advantages obtained by this invention arealso more or less independent of the particular nodularizing agent used(whether or not a further addition of carbon or silicon to the ironbeing treated is made after tapping), although it appears to be moresignificantly useful commercially with the rare earth type of agent thanwith, for example, magnesium.

In connection with the foregoing and the temperatures mentioned itshould be noted that satisfactory results have been attained accordingto this invention in producing finished castings having tensilestrengths of at least the order of 60,000 pounds per square inch andelongations of the order of 10% (both as tested by standard methods)when the carbon equivalent in the finished casting was less than 4.5,and that of the melt prior to they nodularizing addition less than 4 andpreferably less than 3.5 and still with reasonable assurance inproduction foundry techniques of obtaining the desired nodularmicrostruoture routinely and repeatedly.

Whereas the carbon or silicon content of the cold metal added during thechilling step accordihg to this invention may have its effect on theultimate composition of the finished casting, it is believed that theprimary effect according to this invention is one of sudden chilling.

For example, satisfactory results have been achieved in producing theenhanced readiness for precipitation of the carbon by adding, in thechilling steps, such diverse materials as copper, nickel, pig iron, arelatively pure iron such as Arrnco iron, low carbon steels, and nodulariron scrap. Thus, it will be noted that the addition of the cold metalto the molten mix in the ladle need not alter particularly thecomposition of the molten mix, unless desired, and particularly is thistrue when it is realized that, in mass production foundry techniques, asmuch as 50% of the heat may be routinely made up of scrap and sprue fromprevious runs.

It will also be noted that, except for specific temperature adjustmentand whatever adjustment may be necessary in the composition of the mixdepending upon the type of nodularizing or other ladle addition, thepracticing of the process embodying this invention does not requirespecific control or alteration of either the composition of the mix orthe particular nodularizing agent desired, nor need the practicing ofthis invention fundamentally alter the desired nodularizing foundrypractices, although it does provide enhanced assurance of successfulresults, particularly with irons having a low hypoeutectic carbonequivalent as disclosed.

As illustrative of satisfactory results achieved according to thisinvention, one may note data regarding various castings made inaccordance with this invention from an initial molten charge or mixincludng approximately 50% remelted nodular iron, 20% pig iron, and 30%steel scrap. After the starting materials were molten, they were treatedwith a slag comprising high-calcium lime, fluorspar, and coke in theratio of 16%, 5%, and 6% respectively, of the foregoing slag componentson the melt, for the purpose, as will be understood, of enhancing thesusceptibility or responsiveness of the mix to nodularization. Afterbeing held for about 1020 minutes at temperature with the slag, variousportions of the mix were tapped off, subjected to an addition of coldmetal in accordance'with this invention, subjected to an addition ofnodularizing agent, cast, and tested, in accordance with standardprocedures, to produce the data noted in the following tables.

In the various particular instances noted below, the nodularizing agentor additive was a 4-1 combination of calcium silicide and rare earthfluorides followed by a late silicon addition from 75% ferrosilicon(according to, for example, the nodularizing process disclosed in mycopending application S.N. 779,544, filed December 11, 1958). It is tobe understood that comparably enhanced results according to thisinvention are achieved with the use of other nodularizing agents oradditives (e.g., magnesium, misch metal, alloys thereof, etc.).

Table 1 Mins. Percent Percent Percent Heat with Cold metal coldnodularlate Si slag added metal izing agent 10 Nodular Swap. 3 70 1.0 20do 5 .48 1.0 10 .50 1. 0 3 .61 1.0 5 70 5 10 .50 1. 0 3 70 1.0 5 .70 1.08 .50 1.0 10 .46 1. 0 3 .70 .6 3 70 5 Representative castings of theforegoing runs or heats and which produce the data of Table I disclosed,upon analysis and testing by standard methods, characteristics asindicated in the following table:

1 Table II Percent Percent Tensile Elonga- Heat 0 Si O Equiv. BrinellStrength, tion,

p.s.i. Percent The percentage figures in the above tables are weightpercents of the molten mix as analyzed after cold metal addition butbefore the nodular addition, and the physical properties data relate tothe finished castings. The above data and runs or heats or castings areset forth, as noted, merely as illustrative of satisfactory results andoperations according to this invention, although, as will be understoodby men skilled in this art, comparable or equivalent enhanced resultswith other starting mixes, other nodularizing additives, etc.

While the methods, compositions and products described hereinconstitute' preferred embodiments of the invention, it is to beunderstood that the invention is not limited to these precise methods,compositions and products, and that changes may be made therein withoutdeparting from the scope of the invention which is defined in theappended claims.

What is claimed is:

1. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps Which compriseforming in a melting furnace a hypoeutectic molten gray iron rnix havinga low carbon content, heating said mix in said melting furnace to a highfounding and pouring temperature of at least about 2.850 F. fordissolving in said iron substantially all the carbon present in saidmix, withdrawing said thus melted mix from said furnace, adding to saidwithdrawn molten mix solid metal effecting a sudden chilling of about100 Fjof said molten mix by the addition of said solid metal thereto,thereafter treating said mix with a nodularizing agent, and pouring saidthus treated mix into a mold to form said nodular iron casting.

2. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which compriseforming in a melting furnace a hypoeutectic molten gray iron mix havinga low carbon equivalent of less than about 4, heating said mix in saidmelting furnace to a high temperature of at least about 2850 F. andsubstantially above a pouring temperature for said mix for dissolving insaid iron sub stantially all the carbon present in said mix, Withdrawingsaid thus melted mix from said furnace, adding to said withdrawn mix asubstantial portion of solid metal effecting a sudden chilling of about100 F. of said molten mix by the addition of said solid metal theretoand extra addition to said molten mix of undissolved carbon in saidsolid metal, thereafter treating said mix with a nodu larizing agent,and pouring said thus treated mix into a mold to form said nodular ironcasting.

3. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which compriseforming in a melting furnace a hypoeutectic molten gray iron mix havinga low carbon equivalent of no more than about 3.5, heating said mix insaid melting furnace to a high temperature of at least about 2850 F.substantially above a minimal pouring temperature for said mix fordissolving in said iron substantially all the carbon present in saidmix, withdrawing said thus melted mix from said furnace, adding to saidWithdrawn mix a substantial portion of solid metal effecting a suddenchilling of at least about 100 F. of said molten mix by the addition ofsaid solid metal thereto and extra addition to said molten mix ofundissolved carbon in said solid metal, thereafter treating said mixwith a nodularizing agent, and pouring said thus treated mix into a moldto form said nodular iron casting.

4. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which compriseforming in a melting furnaoe a hypoeuteclic molten gray iron mix havinga low carbon equivalent of less than about 4, heating said mix in saidmelting furnace to a temperature of at least about 2850 F. fordissolving in said iron substantially all the carbon present in saidmix, tapping said thus melted mix from said furnace, adding to saidtapped molten mix about 3% by weight solid metal. effecting a suddenchilling of said molten mix by the addition of said solid metal theretoto enhance precipitation of dissolved carbon dur ing final cooling ofsaid mix, thereafter treating said mix with a nodularizing agent, andpouring said thus treated mix into a mold to form said nodular ironcasting.

5. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which compriseforming in a melting furnace a hypoeutectic molten gray iron mix havinga low carbon equivalent of less than about 3.5, heating said mix in saidmelting furnace to a temperature of at least about 2850 F. fordissolving in said iron substantially all the carbon present in saidmix, tapping said thus melted mix from said furnace, adding to saidtapped molten mix about 3% by weight solid metal effecting a suddenchilling of said molten mix by the addition of said solid metal theretoto enhance precipitation of dissolved carbon during final cooling ofsaid mix, thereafter treating said mix with a nodularizing agent, andpouring said thus treated mix into a mold to form said nodular ironcasting.

6. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which compriseforming in a melting furnace a hypoeutectic molten gray iron mix havinga low carbon equivalent of less than about 4, heating said mix in saidmelting furnace to a temperature of about 2850 F. and substantiallyabove a minimal pouring temperature for said mix for dissolving in saidiron substantially all the carbon present in said mix, tapping said thusmelted mix from said furnace, adding to said tapped molten mix about 5%by weight solid metal effecting a sudden chilling of said molten mix bythe addition of said solid metal thereto to enhance precipitation ofdissolved carbon during final cooling of said mix, thereafter treatingsaid mix with a nodularizing agent, and pouring said thus treated mixinto a mold to form said nodular iron casting.

7. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which compriseforming in a melting furnace a hypoeutectic molten gray iron mix havinga low carbon equivalent of less than about 3.5, heating said mix in saidmelting furnace to a temperature of about 2850 F. for dissolving in saidiron substantially all the carbon present in said mix, tapping said thusmelted mix from said furnace, addin to said tapped molten mix about 5%by weight solid metal effecting a sudden chilling of said molten mix bythe addition of said solid metal thereto to enhance precipitation ofdissolved carbon during final cooling of said mix, thereafter treatingsaid mix with a nodularizing agent, and pouring said thus treated mixinto a mold to form said nodular iron casting.

8. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which comp-riseforming in a melting furnace a hypoeutectic molten gray iron mix havinga low carbon content, heating said mix in said meltingfurnace to a highfounding temperature of at least 2850" F. and substantially above aminimal pouring temperature for said mix for dissolving in said ironsubstantially all the carbon present in said mix, tapping said thusmelted mix from said furnace, adding to said tapped molten mix asubstantial proportion of solid metal selected from the group consistingof copper, nickel, pig iron, cast iron, steel, and iron effecting asudden chilling of at least about F. of said molten mix by the additionof said solid metal thereto to enhance precipitation of dissolved carbonduring final cooling of said mix, thereafter treating said mix with anodularizing agent, and pouring said thus treated mix into a mold toform said nodular iron casting.

9. In a process of the character described for the production of nodulariron castings from a molten gray iron mix, the steps which compriseforming in a melting furnace a hypoeutectic molten gray iron mix havinga low carbon equivalent of less than about 4, heating said mix in saidmelting furnace to a temperature of at least about r 285=0 F. fordissolving in said iron substantially all the carbon present in saidmix, tapping said thus melted mix from said furnace, adding to saidtapped molten mix at least about 3% by weight solid metal selected fromthe group consisting of copper, nickel, pig iron, cast iron, steel, andiron effecting a sudden chilling of said molten mix by the addition ofsaid solid metal thereto to enhance precipitation of carbon duringcooling of said mix, thereafter treating said mix with a nodularizingagent, and pouring said thus treated mix into a mold to form saidnodular iron casting,

10. In a process of the character described for the production ofnodular iron castings from a molten gray iron mix, the steps whichcomprise forming in a melting furnace a hypoeutectic molten gray ironmix having a low carbon equivalent of less than about 3.5, heating saidmix in said melting furnace to a temperature of at least about 2850 F.for dissolving in said iron substantially all the carbon present in saidmix, tapping said thus melted mix from said furnace, adding to saidtapped molten mix at least about 3% by weight solid metal selected fromthe group consisting of copper, nickel, pig iron, cast iron, steel, andiron effecting a sudden chilling of said molten mix by the addition ofsaid solid metal thereto to enhance precipitation of carbon duringcooling of said mix, thereafter treating said mix with a nodularizingagent, and pouring said thus treated mix into a mold to form saidnodular iron casting.

11. In a process of the character described for the production ofnodular iron castings from a molten gray iron mix, the steps whichcomprise forming in a melting furnace a hypoeutectic molten gray ironmix having a low carbon equivalent of less than about 4, heating saidmix in said melting furnace to a temperature of at least about 2850 F.for dissolving in said iron substantially all the carbon present in saidmix, tapping said thus melted mix from said furnace, adding to saidtapped molten mix at least about 5% by weight solid metal selected fromthe group consisting of copper, nickel, pig iron, cast iron, steel, andiron effecting a sudden chilling 10 of said molten mix by the additionof said solid metal thereto to enhance precipitation of carbon duringcooling of said mix, thereafter treating said mix with a nodularizingagent, and pouring said thus treated mix into a mold thus melted mixfrom said furnace, adding to said tapped molten mix at least about 5% byweight solid metal selected from the group consisting of copper, nickel,pig iron, cast iron, steel, and iron effecting a sudden chilling of saidmolten mix by the addition of said solid metal thereto to enhanceprecipitation of carbon during cooling of said mix, thereafter treatingsaid mix with a nodulariz ing agent, and pouring said thus treated mixinto a mold to form said nodular iron casting.

References Cited in the file of this patent UNITED STATES PATENTS Eyt etal. Feb. 19, 1952 Moore May 21, 1957

1. IN A PROCESS OF THE CHARACTER DESCRIBED FOR THE PRODUCTION OF NODULARIRON CASTINGS FROM A MOLTEN GRAY IRON MIX, THE STEPS WHICH COMPRISEFORMING IN A MELTING FURNACE A HYPOEUTECTIC MOLTEN GRAY IRON MIX HAVINGA LOW CARBON CONTENT, HEATING SAID MIX IN SAID MELTING FURNACE TO A HIGHFOUNDING AND POURING TEMPERATURE OF AT LEAST ABOUT 2850*F. FORDISSOLVING IN SAID IRON SUBSTANTIALLY ALL THE CARBON PRESENT IN SAIDMIX, WITHDRAWING SAID THUS MELTED MIX FROM SAID FURNACE, ADDING TO SAIDWITHDRAWN MOLTEN MIX SOLID METAL EFFECTING A SUDDEN CHILLING OF ABOUT100*F. OF SAID MOLTEN MIX BY THE ADDITION OF SAID SOLID METAL THERETO,THEREAFTER TREATING SAID MIX WITH A NODULARIZING AGENT, AND POURING SAIDTHUS TREATED MIX INTO A MOLD TO FORM SAID NODULAR IRON CASTING.